This project involves the study of changes in ultrastructure accompanying (1) recovery from short periods of cerebral ischemia and (2) focal freeze lesions of the cerebral cortex of adult cats. Hemorrhagic shock is used to produce cerebral ischemia, and recovery is provided by restoration of the cerebral circulation. Freeze lesions are made by brief exposure of the dura mater to dry ice. The electrocorticogram is recorded during the period of recovery from the injury and prior to fixation for electron microscopy. Various aspects of synaptic structure and neuroglia will be analyzed for qualitative and quantitative changes and will be correlated with recorded electrical events and with progression of the lesions.